P function?

Bob Allen · 01-13-2006, 12:56 PM

Hi: Well, I've had my Prius for almost two years. Last night, my partner borrowed HUMU and asked me a few questions that I should have been able to answer right off, having had HUMU for these two years, etc.

He asked me if (and why) I set the parking brake when parked on level ground. I told him that I've always set the parking brake from the time my uncle taught me to drive on his 58 Rambler stick shift. With a stick shift, it's a hedge against the clutch slipping and the car moving on its own. My partner thought the car "stayed in gear" when you turned it off and that setting the parking brake didn't do much. I pointed out that the owner's manual states that it should be firmly set when parking the car; this might be more for liability issues rather than practical or necessary mechanical reasons.

He also wanted to know what the "P" button did. I told him that it put the car into park, as if it had a conventional automatic transmission, which it does not.

My question is: doesn't the Prius automatically go into "Park" ( = "P") when you push the round Start button to turn the car off? Do you first push the P button before turning the car off?

Bob

aaf709 · 01-13-2006, 01:05 PM

As I understand, if you press the Power button first it will go to Park before powering down. Normally I press the Park button first.

Kiloran · 01-13-2006, 01:15 PM

Quote:

Originally posted by aaf709@Jan 13 2006, 02:05 PM
As I understand, if you press the Power button first it will go to Park before powering down. Normally I press the Park button first.

[snapback]189258[/snapback]

I can confirm that I observed this behavior recently when I accidentally pressed the Power button first.

naterprius · 01-13-2006, 01:38 PM

I have owned my Prius for 15 months and have used the Park button a total of 7 times. I usually just hit the power button to park and power down.

I also ALWAYS set the parking brake. "Park" mode on a transmission is just that, not a very good "car holder". A parking brake is a good car holder.

Marlin · 01-13-2006, 02:04 PM

Quote:

Originally posted by naterprius@Jan 13 2006, 02:38 PM
I also ALWAYS set the parking brake. "Park" mode on a transmission is just that, not a very good "car holder". A parking brake is a good car holder.

[snapback]189285[/snapback]

I never use the parking brake unless I park on a significant hill.

The parking brake advocates often state that "Park" on an automatic transmission is not intended to be used to keep the car from rolling. They say that it is the parking brake instead that is intended to provide that function.

So my question is... If that's true, then why do automatic transmissions even have a "Park" setting? It seems like they wouldn't need anything other than a neutral setting.

SomervillePrius · 01-13-2006, 02:12 PM

This is an interesting discussion.

I never use the parking brake unless parked in a steep slope. My s.o. always does.

I don't see the point as my understanding of the "Park" mode in an automatic is that it keeps the car "in gear" so that you would have to push hard enough for the engine to turn to be able to move it. For a V6 (like on my current Maxima) that would take a lot. My understanding is that stick shifts work the same. I'm sure I might be wrong!

That said how does the "p" button work on the Prius? The Prius has half the engine my Maxima has but a lot of extra weight from batteries. How hard would it be for the Prius to be pushed? and how does it keep the car 'in gear" when no gearbox exsist?

Curious!

richard schumacher · 01-13-2006, 02:27 PM

Quote:

Originally posted by SomervillePrius@Jan 13 2006, 02:12 PM
I don't see the point as my understanding of the "Park" mode in an automatic is that it keeps the car "in gear" so that you would have to push hard enough for the engine to turn to be able to move it. For a V6 (like on my current Maxima) that would take a lot. My understanding is that stick shifts work the same. I'm sure I might be wrong!

That said how does the "p" button work on the Prius? The Prius has half the engine my Maxima has but a lot of extra weight from batteries. How hard would it be for the Prius to be pushed? and how does it keep the car 'in gear" when no gearbox exsist?

[snapback]189317[/snapback]

"P" engages the "parking pawl", a mechanical stop which keeps a gear in the transmission from turning.

I always use "P" for two reasons:

1. Redundancy. It's silly to use just one safety system when two are easily available.

2. Consistency. I never have to decide whether to engage the brake, and I never have to remember whether I need to dis-engage it. I just do it.

Marlin · 01-13-2006, 02:30 PM

Quote:

Originally posted by SomervillePrius@Jan 13 2006, 03:12 PM
I don't see the point as my understanding of the "Park" mode in an automatic is that it keeps the car "in gear" so that you would have to push hard enough for the engine to turn to be able to move it. For a V6 (like on my current Maxima) that would take a lot. My understanding is that stick shifts work the same. I'm sure I might be wrong!

[snapback]189317[/snapback]

No, on an automatic transmission, a car in "Park" is in neutral, but interlocks in the transmission keep the wheels from turning. That's why you can rev the engine with no ill results when it is in Park.

tbstout2 · 01-13-2006, 02:34 PM

When you place a conventional automatic tranny in park it actually engages a gear that locks the car in place. It does not rely on the compression of the engine (like a manual tranny would) to keep the car stationary. However, using the parking brake (BEFORE you place the car in park) gives relief to that particular gear so that the entire weight of the car isn't sitting on that single gear.

I recall my mother struggling to get her '68 Bel Air wagon out of park when it was sitting on a hill (and she hadn't used the parking brake). My dad told her to use the parking brake so that it wouldn't happen in the future.

I'm sure everyone has noticed that when you put a car in park the car may move backward or forward depending on the grade of the pavement. At that point the car is, technically, safe to leave just like that.

The Prius has a similar "park" gear. It will remain stationary when in "park", but it's always a safe measure to use the parking break. Another reason to use the parking brake: The "P" function locks the front wheels. The Parking Brake locks the back wheels. Therefore you have double the "locking" power!

tbstout2 · 01-13-2006, 02:36 PM

Quote:

Originally posted by Marlin@Jan 13 2006, 02:30 PM
No, on an automatic transmission, a car in "Park" is in neutral, but interlocks in the transmission keep the wheels from turning. That's why you can rev the engine with no ill results when it is in Park.

[snapback]189335[/snapback]

Actually, when my Prius is in "P", and I rev the engine, the car DOES rock a wee-little bit!

01-13-2006, 12:56 PM	#1
Bob Allen Captainbaba Join Date: Jan 2004 Location: Seattle, WA Posts: 1,254 My Car: 2004 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Hi: Well, I've had my Prius for almost two years. Last night, my partner borrowed HUMU and asked me a few questions that I should have been able to answer right off, having had HUMU for these two years, etc. He asked me if (and why) I set the parking brake when parked on level ground. I told him that I've always set the parking brake from the time my uncle taught me to drive on his 58 Rambler stick shift. With a stick shift, it's a hedge against the clutch slipping and the car moving on its own. My partner thought the car "stayed in gear" when you turned it off and that setting the parking brake didn't do much. I pointed out that the owner's manual states that it should be firmly set when parking the car; this might be more for liability issues rather than practical or necessary mechanical reasons. He also wanted to know what the "P" button did. I told him that it put the car into park, as if it had a conventional automatic transmission, which it does not. My question is: doesn't the Prius automatically go into "Park" ( = "P") when you push the round Start button to turn the car off? Do you first push the P button before turning the car off? Bob __________________ :P Angel Flight Pilot

01-13-2006, 02:12 PM	#6
SomervillePrius Senior Member Join Date: Jan 2006 Location: Somerville, MA Posts: 946 My Car: 2006 Prius Package: #9 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	This is an interesting discussion. I never use the parking brake unless parked in a steep slope. My s.o. always does. I don't see the point as my understanding of the "Park" mode in an automatic is that it keeps the car "in gear" so that you would have to push hard enough for the engine to turn to be able to move it. For a V6 (like on my current Maxima) that would take a lot. My understanding is that stick shifts work the same. I'm sure I might be wrong! That said how does the "p" button work on the Prius? The Prius has half the engine my Maxima has but a lot of extra weight from batteries. How hard would it be for the Prius to be pushed? and how does it keep the car 'in gear" when no gearbox exsist? Curious! __________________ help start a revolution! Demand PLUG IN Hybrids to be built today!

01-13-2006, 02:34 PM	#9
tbstout2 Senior Member Join Date: Jun 2005 Location: Northern, VA Posts: 153 My Car: 2005 Prius Package: #2 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	When you place a conventional automatic tranny in park it actually engages a gear that locks the car in place. It does not rely on the compression of the engine (like a manual tranny would) to keep the car stationary. However, using the parking brake (BEFORE you place the car in park) gives relief to that particular gear so that the entire weight of the car isn't sitting on that single gear. I recall my mother struggling to get her '68 Bel Air wagon out of park when it was sitting on a hill (and she hadn't used the parking brake). My dad told her to use the parking brake so that it wouldn't happen in the future. I'm sure everyone has noticed that when you put a car in park the car may move backward or forward depending on the grade of the pavement. At that point the car is, technically, safe to leave just like that. The Prius has a similar "park" gear. It will remain stationary when in "park", but it's always a safe measure to use the parking break. Another reason to use the parking brake: The "P" function locks the front wheels. The Parking Brake locks the back wheels. Therefore you have double the "locking" power! __________________ China will own the US if we don't stop borrowing for Bush's War! 2005 Black Pkg 2 MODS: Mudguards, side door trim, stiffening plate, window tint, bumper step cover AND the wonderful DICE unit. This car looks (and sounds) sharp!

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01-13-2006, 01:05 PM	#2
aaf709 Ravenpaw of ThunderClan Join Date: Apr 2005 Location: San Diego, CA Posts: 3,838 My Car: 2005 Prius Package: #6 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	As I understand, if you press the Power button first it will go to Park before powering down. Normally I press the Park button first.

01-13-2006, 01:38 PM	#4
naterprius Senior Member Join Date: Mar 2004 Location: USA Posts: 1,830 My Car: Other Non-Hybrid Package: N/A Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I have owned my Prius for 15 months and have used the Park button a total of 7 times. I usually just hit the power button to park and power down. I also ALWAYS set the parking brake. "Park" mode on a transmission is just that, not a very good "car holder". A parking brake is a good car holder.